In a small and high-power motor (an electric motor), heat generation when it is in operation is disregarded, and sometimes a malfunction such as a burned-out winding of the motor occurs.
Conventionally, as a water-cooled structure for a motor, suggested is a cooling system for an electric motor in which a passage for cooling water is provided in a space between an inner cylinder and an outer cylinder of a cylindrical frame for which a stator and a rotator are fitted therein (Patent Literature 1). This system includes a configuration in which a plurality of partition walls is provided on the passage for the cooling water along the axial direction of the cylindrical frame such that the cooling water supplied from an inlet conduit for the cooling water is guided to an outlet conduit for the cooling water, while the direction of the flow of the cooling water is alternately changed between the side of one end and the side of the other end of the cylindrical frame. Similar configurations are disclosed in Patent Literature 2 and 3.